1. Field of the Invention
The present invention relates to a scintillation camera for radiographing a two dimensional distribution image or a tomographic image in accordance with a radioactive isotope distributed in a body for examination, and more particularly, relates to a scintillation camera including a modified collimator exchanger for changing collimators attached to detectors.
2. Description of the Prior Art
FIG. 1 explains the principle of a conventional scintillation camera. As seen in the figure, gamma rays 11 radiated from the examined body P cause the scintillator 13 to emit fluorescent rays proportional to the energy of the gamma rays. The fluorescent rays are guided to a plurality of photomultiplier tube (PMT) 17 through a light-guide 15 and are changed to electric pulses proportional to the energy level of the fluorescent rays in the PMT. A unit consisting of a scintillator, a light guide and photomultiplier tubes is referred to as a detector 19 hereinafter. The pulses from the detector 19 are processed by a processor 21 to form a tomographic image having a two-dimensional distribution. The tomographic image is displayed on a display unit 23.
In the above device, a collimator 25 is used which only accepts gamma rays which are parallel to its holes and blocks other gamma rays such as a gamma ray entering the collimator openings obliquely. Various kinds of collimators are usable for this purpose. For example, a collimator for high, medium or low energy can be used depending upon the energy of the radioactive isotope. Collimators with different sized openings are used depending upon the required resolution and sensitivity of the images. To be used properly, collimators must be changed according to the radiographic purposes.
A conventional scintillation camera includes a plurality of detectors with collimators attached for parallel processing. A conventional collimator exchanger changes all collimators simultaneously for an efficient exchange. A conventional collimator and holding device is described in U.S. Pat. No. 5,059,799 assigned to the same assignee of the present application. This conventional collimator exchanger comprises a carrier with rails and a holding device for holding collimators. In FIGS. 2A and 2B, the collimator is provided with a screw hole 31, pin holes 33, guide pins 35, a through hole 37 and includes for example, 2000 to 4000 of collimator holes 39.
In FIG. 3, the holding device for holding the collimators comprises a frame 41 secured to a carrier, a first block 43 consisting of upper and lower halves each secured to the frame 41, a second block 45 with a through hole 47 and sliding parts 49 joined to the first block and movable in the Y axis and Z axis directions in the figure, a flat member 51 with a flat surface for attaching the collimator, and an attaching screw 53 for attaching the collimator to the holding section.
In the above-mentioned holding device, the collimators are fully secured to the holding device and are not swingable. Considerable time and trouble are required to attach or detach a plurality of collimators when the detectors are placed in an improper position.
For example, it is sometimes difficult to attach the collimators to an attaching section when the levels of the attaching sections do not agree with the levels of the collimators supported by the holding device, or in which the collimators or the attaching sections are inclined. The problem becomes more serious in a scintillation camera with a plurality of collimators and detectors when they are exchanged simultaneously.